If set to yes, then the number refers to the canceling key signature specified by the <cancel> element in the
parent <key> element. It cannot be set to yes if there is no corresponding <cancel> element within the
parent <key> element. It is no if absent.
number: number
A positive integer that refers to the key signature element in left-to-right order.
If set to yes, then the number refers to the canceling key signature specified by the
<cancel>element in the parent<key>element. It cannot be set to yes if there is no corresponding<cancel>element within the parent<key>element. It is no if absent.